62 



HYDROGRAPHY. 



[Sect. Ill 



of the log line to it, and veer away both together.* Tlien 

 mark by a watcli the time each knot is in ruimino- out 



buoying up the lii 





a chip of wood ; when all the 



line has rim out, take the bearing of the nipper by a 

 compass, imd haul all in together. If currents be tried 

 when there are no soundings, the result is merely the 

 relative motions of the upper and lower strata of the Mater, 

 and it would be difficult to say which way either 



were 



oing ; but if we can possibly determine by astronomical 

 observations the course of the upper surface, we shall 

 thence be able to deduce the set of the lower ; and if there 

 be found any difference of moment, it will be very desirable 



of both upper and lower 

 strata of the water, and to record them with the other 



to ascertain the temnerature 



These 



observations. 



made on calm days, and th 



observations ought always to be 



j^j 



greater 



the weight be sunk, the better. Bottles thrown over- 

 board with a label inside. 



and lonff. 



5. of the spot where c;xb 



containing the date and lat. 



5t into the sea. afford 



ready means of detecting the current if picked up after 



wards, and ships would do well frequently to expend a 

 few empty bottles in this way.f In the event of meeting 

 any such drifting at sea, they should be picked up, their 

 contents copied, and the date and position of the spot 

 added to the label and carefully resealed, they should 

 then be returned to the ocean, and a copy of the label 

 forwarded to the hydrogTapher. 



* If the lead-line be not hitched to the nipper, the tide may drag the 

 line through it, and there will be no result. 



t The bottles, before sealed, should be ballasted ^ith a little dry sand, 

 consohdatea at the bottom with bees'-wax or pitch run in, that the bottle 

 may be Itept upright and not swim too light. 



h 



I 



f 





i 



Sect- II 



8. 



the dr 

 one * 



or a^ 



time 1 



noting 

 Sue 



cumst 



%J 



ever 1 



sliouk 



. ■ 



times 



or vr 



lions : 



will ^ 



Laic ^. 



V 



i-vv i.--. \J 



portai 

 of the 



of h.^. 



Outgc' 



iti 



^ater, 



\ 



-'a 



le 



Tl 



fefern 

 probe,' 

 and tl 



one 



0: 



the t:. 



